1. Field of the Invention
The present invention relates to a steering angle sensor unit mounted on a steering shaft of a motor vehicle and the like to detect information about the turn of a steering wheel and to electrically connect electric devices mounted on the steering wheel and a vehicle body.
2. Description of the Related Art
Hitherto, a device called a steering angle sensor unit has been proposed which includes a combination of a steering angle sensor for detecting information about the turn of a steering wheel and a rotary connector for electrically connecting an electric device mounted on the steering wheel and an electric device mounted on a vehicle body.
A steering angle sensor detects the steering angle and the steering direction of the steering wheel, and uses these to control the damping force of the suspension, the shift position of the automatic transmission, and the steering of the rear wheels of a four-wheel steering (4WS) vehicle. In general, the steering angle sensor comprises a code plate mounted on a rotor section that is rotationally driven by the steering wheel, and a light emitting device and a photoreceptor mounted inside a casing for forming a stator section. On the other hand, a rotary connector permits the electrical connection between an electric device mounted on the steering wheel serving as a rotary member, and an electric device mounted on a vehicle body serving as a fixed member. In some rotary connectors, a flexible electric cable or optical fiber cable (hereinafter generically referred to as "flexible cable") is wound and held between a rotor section to be rotationally driven by the steering wheel and a casing for forming a stator section, the flexible cable being fixed to the rotor section at one end and to the stator section at the other end, and the electrical connection between the electric devices is permitted by winding and rewinding the flexible cable.
A conventional steering angle sensor unit will now be described.
FIG. 11 is a structural sectional view of a conventional steering angle sensor unit taken along line 11--11 in FIG. 12, FIG. 12 is a structural sectional view taken along line 12--12 in FIG. 11, and FIG. 13 is a structural sectional view taken along line 13--13 in FIG. 12.
As shown in FIGS. 11 to 13, a steering angle sensor unit 80 comprises a rotor member 52 that is fixed to a steering shaft (not shown) of a vehicle and that turns with the operation of a steering wheel (not shown), a first casing 53 spaced around the rotor member 52 at a predetermined interval and having a smooth inner peripheral surface to serve as a stator member, a flexible cable 54 for forming a rotary connector, a winding core 56 fitted in or integrally formed with a second casing 55 having a smooth inner peripheral surface to wind the flexible cable 54 thereon, and the like.
The first casing 53 and the second casing 55 are integrally formed, and the second casing 55 is spaced around the winding core 56 at a predetermined interval. A winding-assist member 57 that can turn coaxially with the winding core 56 is disposed between the second casing 55 and the winding core 56 at predetermined distances therefrom. A wall 58 is disposed between the first casing 53 and the second casing 55, and a cable path 59 is formed at the end of the wall 58.
In the steering angle sensor unit 80 having such a configuration, a steering angle sensor 70 contains a rotary connector 71.
A description will now be given of the structure and placement of the steering angle sensor 70 in the steering angle sensor unit 80.
Fixed to the rotor member 52 is a slit plate 60 having through holes 60a that are spaced at predetermined intervals in the circumferential direction. A photo-interrupter 61 is placed in the first casing 53 that does not move with the steering wheel being operated, and includes a photoreceptor 62 and a light emitting member 63 that sandwich the outer peripheral portion of the slit plate 60 and the through holes 60a. The photo-interrupter 61 also has a printed circuit board 64 for detecting signals that are output when the slit plate 60 blocks or passes the light travelling from the light emitting member 63 toward the photoreceptor 62.
The rotor member 52 having the slit plate 60 fixed thereto is loosely fitted with a clearance in holes 53c and 53d formed through an upper wall 53a and a lower wall 53b of the first casing 53. The printed circuit board 64 is connected to both the photoreceptor 62 and the light emitting member 63, and is provided with a power supply circuit (not shown) for supplying electric power to the photoreceptor 62 and the light emitting member 63, and the like.
The structure of the rotary connector 71 will be next described.
One end of the flexible cable 54 is fixed to the rotor member 52 serving as a rotor in the steering angle sensor 70.
The other end of the flexible cable 54 is wound on the winding core 56, fixed to the second casing 55, and electrically connected to an external output connector that is not shown.
Next, a description will be given of the operation of the steering angle sensor unit 80 having the configuration mentioned above.
First, when the steering wheel (not shown) is operated, the rotor member 52 in the steering angle sensor unit 80 turns. Thereby, the slit plate 60 also turns. With the turn of the slit plate 60, light emitted from the light emitting member 63 in the photo-interrupter 61 is blocked by or passed through the through holes 60a of the slit plate 60 that turns between the light emitting member 63 and the photoreceptor 62. A detection signal (photocurrent) output from the photoreceptor 62 based on the light thus passed or blocked is output via an electric circuit formed on the printed circuit board 64.
Based on this output signal, the turn angle of the steering shaft is calculated in a central processing unit (CPU), which is not shown, and the like. The turn angle of the steering shaft represents the steering amount or the steering angle of the steering wheel that is operated by a passenger in turning the vehicle. The turn state of the vehicle, the lateral acceleration of the vehicle body in the lateral direction, or the like is detected by using such calculated values, and this is used to control the vehicle in order to improve the stability of running of the vehicle or the riding comfort of the passenger, for example, to control the suspension.
When the rotor member 52 turns, the flexible cable 54 for constituting the rotary connector 71 is wound around the rotor member 52 or rewound. This flexible cable 54 electrically connects an electric device on the side of the steering wheel and an electric device on the side of the vehicle body.
The rotary connector generally comprises a pair of housings coupled so that they can relatively turn, and a flexible cable wound in an annular storage space defined between the housings. Both ends of the flexible cable are electrically led outside while they are fixed to the housings. One of the housings is used as a rotor member, and the other is used as a stator member. When the rotor member is turned in the forward or reverse direction, the flexible cable is wound up or rewound inside the storage space, depending on the turning direction.
The rotary connector having such a structure is incorporated in a steering device of a motor vehicle, and used as a connecting means for electrically connecting a steering wheel and a column. In this case, a known mounting structure is widely adopted, in which a rotor member in a rotary connector is connected to a steering wheel and a stator member in the rotary connector is attached to a combination switch on the side of a column. This combination switch contains various switch units, such as a head-lamp switch and a wiper switch. In general, the head-lamp switch is provided with an indicator cancel mechanism for causing a control lever at the right or left working position to automatically return to the center position.
In a well-known manner, a cancel cam is formed at a part of the rotor member that projects from the bottom face of the stator member in the rotary connector, and a cancel lever in the indicator cancel mechanism is put into the turn area of the cancel cam, whereby the indicator cancel mechanism is operated by using the turning force of the rotor member. In this case, when the steering wheel is turned to the neutral position, since the rotor member in the rotary connector turns along with the steering wheel, the cancel lever is driven by the cancel cam of the rotor member, and the control lever thereby automatically returns to the center position.
In the steering angle sensor unit having the configuration mentioned above, however, the rotor member 52, to which the slit plate 60 is fixed, functions as both a rotor member in the steering angle sensor 70 and a rotor member in the rotary connector 71, and is loosely fitted with a clearance in the holes 53c and 53d that are formed through the upper wall 53a and the lower wall 53b of the first casing 53. This is because the rotary connector 71 contains the flexible cable 54 and it does not stably turn when the flexible cable 54 is wound or rewound unless a predetermined clearance is ensured. Therefore, there is a need to provide some play between the rotor member and the stator member in the rotary connector 71. On the other hand, if there is a large clearance between the rotor member and the stator member in the steering angle sensor 70, the rotation axis of the rotor member substantially deviates (offsets in the axial and radial directions). Since the slit plate 60 is fixed to the rotor member, the position of the slit passing between the photoreceptor 62 and the light emitting member 63 substantially changes, whereby the detection signal, obtained by the passage and block of light between the light emitting member 63 and the photoreceptor 62 with the turn of the slit plate 60, fluctuates and is not stable. In recent years, the steering angle sensor 70 has been required to have higher precision and higher resolution, and the adverse effect of the play is not negligible.
Furthermore, the stator member and the rotor member that are constituents of the rotary connector are not closely coupled to each other, and, in general, the rotor member is turnably coupled with some clearance with respect to a guide hole of the stator member so that this clearance absorbs the measuring errors and the mounting errors of the components. Therefore, there is a fear that the rotor member will turn within the clearance at an inclined angle with respect to the center axis of the stator member mounted on a casing of the combination switch. If the cancel cam is formed at the projecting portion of the rotor member, as in the related art mentioned above, the cancel cam and the cancel lever are prone to relative offset, thereby disabling the cancel lever.